1. Field of the Invention
The present invention relates to an improvement in an electronic desk-top calculator having a unit conversion function, and more particularly to an electronic desk-top calculator with a unit conversion function (hereinafter referred to as a unit conversion desk-top calculator)which selects a type of conversion having a highest frequency of usage from a plurality of types of conversion and stores it so that the conversion in accordance with the stored type of conversion is carried out by merely actuating a key for specifying a direction of conversion.
2. Description of the Prior Art
FIG. 1 shows an external view of a prior art unit conversion desk-top calculator. Numeric data is entered by numeric keys on a keyboard 3 and calculated by instructions entered by operation instruction keys. A conversion direction specifying key 4 or 5 is depressed to specify the direction of conversion, rightward or leftward, that is, from the foot/pound system to the metric system or vice versa in the example shown in FIG. 1. Then, a desired type of conversion is selected by depressing one of conversion keys 6, which also serve as the numeric keys or the function keys, to carry out the desired conversion. For example in order to convert 2 inches to centimeters the prior art unit conversion desk-top calculator needs the following keying operations.
FIG. 3A shows the keying sequence. In a step 1, a numerical value "2" to be converted is entered. It represents 2 inches and it is to be converted to centimeters. In a step 2, the right conversion key ".fwdarw." is depressed to specify the conversion from the foot/pound system to the metric system. Since the conversion desired is the inch to cm conversion, a numeric key 7 is depressed in the step 3.
As a result, an arithmetic operation control circuit in a main body carries out a multiplication operation to multiply the entered numerical value by 2.54 which is the conversion rate for the inch to cm conversion (1 inch=2.54 cm) under the control of a program stored in a ROM and display a result 5.08.
In this manner, the inch to cm unit conversion process is carried out. As shown in the steps following step 3 of FIG. 3A, when only the numerical value to be converted is changed, for example, when 3 inches is to be converted to centimeters, numerical value "3" is entered in a step 4, the right conversion key ".fwdarw." is depressed in a step 5 and the key 7 is depressed in a step 6. Thus, the entered numerical value "3" is multiplied by 2.54 and a result 7.62 is displayed, in the same manner as the steps 1 to 3. When it is desired to convert 2.54 cm to inches, that is, an opposite direction convertion is desired, a numerical value "2.54" is entered in a step 7, a left conversion key ".rarw." is depressed in a step 8 and the key 7 which is the inch to cm conversion key is depressed in a step 9. Thus, the arithmetic operation control circuit issues an instruction to divide the entered numerical value by the conversion rate 2.54 and displays a result 1. In a step 10, an ordinary multiplication operation of 2.times.3=6 is carried out. In steps 11-13 and steps 14-16, 4 inches and 5 inches, respectively, are converted to centimeters.
As seen from FIG. 3A, in the prior art keying sequence, three steps of keying, that is, entering of the numerical value, specification of the conversion direction and specification of the type of conversion are needed for each conversion operation. When an operator repeatedly carries out the conversion operation of the same type, the same keying sequence must be repeated. Consequently, the efficiency of operation is very poor.